Test it

npm install
npx playwright install chromium
npm test                                   # 26 tests, ~3s
npx playwright test --ui                   # watch mode with time-travel debugging
npx playwright test --repeat-each=10       # flake check (251/251 when written)

The tests start their own server on port 3101 with NODE_ENV=test, which enables the /__test__/orders data factory. The "model" is a deterministic stand-in so the app and the tests run offline; §63 shows how to swap in WebLLM or an edge-hosted open-weight model behind the same event protocol.